Titanium silicide-coated glass windows

ABSTRACT

Transparent glass windows comprising thereon titanium silicide (TiSi 2 ) as the principal solar screening layer for reducing transmission of near infrared and visible radiation. In some embodiments, a protective layer of silicon or metal oxide, about 300 angstroms thick, is placed thereover. The protective layer serves to protect the silicide from oxidation during high-temperature processing procedures and increases the abrasion-resistance of the window product. The particular importance of titanium silicide film is that it allows production of a window that is neutral in color when viewed in transmission as well as in reflection. Thus, one is able to provide a durable, pyrolytic, high-performance, color-neutral, solar-shielding window product.

This is a divisional of co-pending application Ser. No. 07/182,092 filedon Apr. 15, 1988 now U.S. Pat. No. 5,057,375.

BACKGROUND OF THE INVENTION

This invention relates to the improvement in providing transparent,color-neutral, glass window products particularly those used inshielding windows from excessive solar heat gain during warm weather.

Control of the solar energy entering through window areas of a buildingis important in maintaining comfortable indoor conditions in warmclimates. Solar control has been achieved by adding light-responsivecolorant materials to the glass. Tinting of glass in this way hasdisadvantages in production, however, since a long time may be requiredto change shades More recently, reflecting and absorbing films have beenapplied to clear glass, to achieve solar control. Reflection of unwantedradiation is more efficient than absorption, since reflection eliminatesthe radiation completely, whereas part of the absorbed heat iseventually carried into the building.

It has also been proposed in U.S. Pat. No. 3,885,855 to produce solarcontrol films by reactive sputtering of the nitrides, carbides orborides of the metals titanium, zirconium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum, or tungsten. While effective opticalproperties were achieved for some of these materials, any large-scaleproduction of architectural glass by the vacuum electrical method ofreactive sputtering would be rather slow and expensive.

In U.S. Pat. No. 4,535,000 issued on Aug. 12, 1985, Roy G. Gordondisclosed a rapid process for deposition of transparent solar screens oftitanium nitride while avoiding haze and imperfections on the sheetbeing coated. These improvements in titanium nitride depositionprocedures did not avoid some inherent problems in achieving broadacceptance of TiN as a solar-shielding, glass-coating material in suchmarkets as architectural glass. These problems included somesusceptibility to mechanical and chemical attack and some limitationswith respect to visual characteristics of TiN film, particularly thetendency to show colors in transmission, i.e. the TiN-window product asnormally viewed by building occupants from inside.

Titanium-silicide-type coatings had previously been considered for useas a coating on glass. For example, Varapath in U.S. Pat. No. 4,696,834describes a TiSi₂ on glass as having a silvery reflection. It is one ofthe many dozens of films Varapath suggested or investigated indescribing a new CVD process. Also, Gross in U.S. Pat. No. 3,885,855mentions silicides and, inferentially as part of Group IV PeriodicTable, titanium silicide for solar coatings. Neither of these partiesrecognized any particular value to the properties of titanium-silicidecoatings with respect to such films as titanium nitride coatings.

In general, it is fair to say that those investigators of the prior art,and others too, have failed to find anything about TiSi₂ coatings whichwould make it a particularly desirable commercial coating for windowsand qualitatively differentiate it from comparable solar-shieldingcoatings such as the TiN coatings described in U.S. Pat. No. 4,535,000to Gordon.

In fact, however, and as described below, the present inventor hasdiscovered that the composite properties of certain TiSi₂ -coated glassproducts make them unique in solar-shielding applications. Inparticular, they have been found to be advantageous in transmittedappearance over the previously-favored titanium nitride films.

Another type of solar-control window, one based on coatings offluorine-doped tin oxide, is disclosed in Gordon's U.S. Pat. Nos.4,265,974 and 4,146,657. Such tin oxide coatings are particularlyvaluable when high solar transmission and very low emissivity isdesired, i.e. when one wishes to reduce winter heating costs. Thewindows of the present invention have lower solar transmission as wellas low emissivity, and are preferred for many applications when economicair-conditioning of a building is an important factor.

It is to be noted that the art cited in this "background section" hasnecessarily been cited using the present invention as a guide incollection and interpretation of said prior art. It is not to beinferred that such diverse art would be collected without use of theinvention described herein as a guide for such collection.

SUMMARY OF THE INVENTION

All of U.S. Pat. Nos. 4,535,000; 4,265,974, 4,690,871 and 4,146,657 areincorporated herein by reference.

A principal object of the invention is to provide an improved solar filmcharacterized by good solar-shielding-window properties and a neutralcolor when viewed by transmitted light.

Another object of the invention is to obtain a window as described abovewhich is also color-neutral when viewed by reflection.

Another object of the invention is to provide oxidation protection ofTiSi₂ film during high-temperature processing of glass sheets upon whichthe film has been deposited.

Another object of the invention is to provide a titanium-silicide-basedsolar shielding window which has excellent abrasion resistance,excellent oxidation resistance after being formed in a float-glass-bathapparatus or when subjected to high-temperature annealing, tempering, orbending procedures.

Another object of the invention is to provide a process for using TiSi₂as a solar shield on architectural windows, to reduce the solar heatgain during hot weather.

Other objects of the invention will be apparent to those skilled in theart on their reading of this disclosure.

The above objects have been substantially achieved by forming windowsbearing titanium silicide film as the principal barrier to near infraredand visible radiation. In some embodiments of the invention, thesilicide coating is covered with a coating of a protective transparentfilm, advantageously tin oxide. This use is analagous to that disclosedfor TiN-type coatings in U.S. Pat. No. 4,690,871 to Gordon. Otherprotective films may be used over the TiSi₂. For example, silicon,silicon oxide and aluminum oxide have good protective properties.However, tin oxide and silicon films, particularly fluorine-doped tinoxide, are believed to have the most favorable combination ofmechanical, optical and infrared emissivity properties to complementsolar-shield applications of TiSi₂ -coated windows. The tin oxide filmsare preferable for use as protective coatings on high-light-transmissionglass sheets, e.g., those coated over a 200 angstrom thick TiSi₂ film.An example would be primary vision areas of automotive glass which musthave a visible light transmission of about 70%. In any event, theprotective coatings should provide adequate protection of the windows atannealing and tempering temperatures of 1000° F. and above.

It should be understood that the term TiSi₂ relates to coatingscontaining principally titanium-silicide but there may be someimpurities therein in a quantity that does not interfere substantiallywith the advantages, described herein, of TiSi₂ -coated window products.

In lower-transmission applications (e.g., an automotive sun roof orarchitectural glass) a titanium silicide thickness of about 500angstroms, preferably in combination with a 300 angstrom overcoat filmof tin oxide, would provide a highly-suitable combination for obtaininga 13% visible transmission.

Thus, among preferred products of the invention are transparent glasssheets comprising thereon titanium-silicide as the principal solarscreening layer for reducing transmission of near infrared and visibleradiation and, thereover, a layer of thin protective film of metal oxideor silicon of about 100 to 400 angstroms thick. The tin oxide layers areespecially suitable to protect the titanium silicide from oxidationduring high-temperature processing procedures, e.g. such as tempering,bending and annealing of the glass at temperatures over 1000° F., andincreases the abrasion-resistance. Protective layers of about 300angstroms or higher are preferred.

The performance of these solar-control coatings is only slightlydependent on the glass substrate on which they are placed and from whichwindows are to be made. However, more exact values of optimum thicknessof both the silicide and any protective coating can be determined foreach application of the invention after one selects a particularsubstrate and the desired parameters for emissivity, solar transmission,and visible transmission.

In one advantageous application of the invention, an ancillarytitanium-nitride based coating is sandwiched between two protectivecoatings of titanium silicide. In such systems, the titanium nitridefilm serves the principal function of helping to reduce near-infrared(wavelengths of from about 0.7 to 2 microns) transmission without losingmuch in transmission of visible wavelengths. However, the undesirabletransmission colors of the titanium nitride are very much reduced by theuse of a major portion of titanium silicide in the coating. A protectivelayer over the silicide still serves to increase the abrasion resistanceand serves as an oxidation-protective layer during manufacture and afterthe coating operation itself, in subsequent high-temperature fabricationsteps such as annealing, tempering or bending processes. In suchapplications, it is preferred to keep the total coating thickness (lessany protective layer) under 600 angstroms. This gives adequate solarprotection in almost all applications and is a product that can beformed very conveniently on continuous processing equipment, e.g. floatglass production lines.

TiSi₂ films of about 300 to 800 angstroms in thickness have neutral,i.e. silver, reflection color. Moreover, this neutral color ismaintained at different thicknesses of the TiSi₂ coating. Thus, thewindows of the invention have a neutral tone, an aesthetic propertymuch-sought-after in solar-control windows, when viewed from eitherside.

The protective-coated silicide products of the invention are highlyadvantageous because of the combination of solar-shielding propertiesand the fact that they are neutrally-colored when viewed in transmission(e.g. a very light gray, which becomes darker as the thickness isincreased) and the superior abrasion resistance of tin oxide relative toTiSi₂. However, the use of a protective coating such as tin oxide isparticularly important in processing procedures. Thus, for example,transparent glass products prepared according to the invention can beannealed at typical glass-plate annealing temperatures of 1000° F. foran hour without any significant, or even detectable, oxidation of thesolar-control film. Similarly, tempering at temperatures of about 1150°F. for five minutes results in no deterioration of the product.

Another important process aspect of the invention is the processingadvantage associated with the conservation of titanium silicide coatingwhich might otherwise be lost to oxidation during the process of coatinghot glass with TiSi₂ according to such high-temperature coatingprocedures as described in U.S. Pat. No. 4,535,000. In such a procedure,and assuming the titanium silicide film would take about 20 seconds tomove 10 feet from the exit of a float bath to a tin-oxide overcoating,then substantial titanium silicide could be oxidized to titanium oxide.Such a loss of TiSi₂ can often be tolerated or compensated for. But, itintroduces a wholly unnecessary variable into the process.

The protective coating is of particular value in avoiding theabove-described loss of silicide during the coating operation. Suchconversion of silicide to oxide also introduces another variable intothe product and may result in tone variations in the product as it issubjected to post-coating annealing and tempering. Tin oxide offersparticular value in protecting the newly-formed titanium silicide fromoxidation during annealing and tempering operations at temperaturesexceeding 800° F. and, typically between 1000° and 1200° F.

Consequently, the overcoating of the silicide with tin oxide isadvantageously, although not necessarily, carried out in the atmosphereof the tin bath structure in which the glass sheet to be coated isformed. This procedure allows the required amount of silicide to be usedmore efficiently as a solar shield and to be deposited more rapidlybecause no significant allowance need be made for oxidation.

The titanium disilicide films are readily formed by the reaction oftitanium chloride and monosilane. The reaction occurs rapidly attemperatures typical of a float bath in glass-protection operations ofthe "float-glass" type wherein the glass is formed on a layer of liquidmetal. Coating formation rates of above 300 angstroms per second areattainable in the float bath environment without unduly slowing theproduction line. Indeed, rates of above 400 angstroms per second can beachieved, and it is believed no prior art process allowed such rates tobe achieved while achieving optically-clear coatings suitable for windowglass.

A typical reaction mixture is about 1% TiCl₄, 3% SiH₄ and the balance aninert gas, preferably helium. These percentages are in terms of moles,not weight. These can be easily mixed at temperatures not much aboveroom temperature (i.e. above the dew point of TiCl₄), and the mixture isreasonably stable and can be transported at temperatures up to about900° F. (about 482° C.). Much above 900° F., there is the possibility ofpremature formation of TiSi₂ dust by reaction of the stored mixture'scomponents.

The reaction to form a TiSi₂ coating occurs rapidly above above 1200°F., desirably at about 1250° F. (about 677° C.). Most of the heat comesfrom the glass which is about 1250° F.

The TiSi₂ -coated windows of the invention have better (lower) shadingcoefficient than do silicon films of equal visible transmission, andhave surprisingly high absorption and/or reflection throughout thevisible spectrum and into the near infrared spectrum. The films do nottend to display interference colors as they are made thicker. Thus,thickness adjustments can be made to obtain the desired amount ofsolar-shielding without having to make any other process changes tomaintain color neutrality.

It is often desirable to form a very thin silicon precoat--as is knownin the glass producing art--between the glass substrate and the TiSi₂coating in order to reduce the probability of haze being created byreaction of chlorine (from the TiCl₄) and sodium in the glass. Such asilicon precoat also improves the properties of the TiSi₂, increasingits electrical conductivity and infrared reflectivity, and decreasingits emissivity.

ILLUSTRATIVE EMBODIMENT OF THE INVENTION

In this application and accompanying drawings there is shown anddescribed a preferred embodiment of the invention and suggested variousalternatives and modifications thereof, but it is to be understood thatthese are not intended to be exhaustive and that other changes andmodifications can be made within the scope of the invention. Thesesuggestions herein are selected and included for the purposes ofillustration in order that others skilled in the art will more fullyunderstand the invention and the principles thereof and will be able tomodify it and embody it in a variety of forms, each as may be bestsuited to the condition of a particular case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a specific embodiment of the invention.

FIG. 2 illustrates an embodiment of the invention comprising the use ofa titanium nitride layer between two titanium silicide layers.

FIG. 3 illustrates a reactor-coater apparatus useful in making theproduct.

FIG. 1 illustrates schematically, a transparent solar-shield windowproduct 88 held in a frame 120 suitable for use as architectural glassand comprising a soda lime glass substrate 90, a coating 82 of about 400angstroms of TiSi₂, and a protective coating of 300 angstroms offluorine-doped tin oxide 84. The tin oxide coating is achieved usingreactant system for SnO₂ known in the art, e.g. that described in U.S.Pat. Nos. 4,265,974 and 4,146,657.

The structure according to FIG. 1 is modified by replacing the tin oxidewith 200 angstroms silicon, in one instance, and 200 angstroms aluminumoxide in another instance. Both of these oxides form good protectivecoatings over the tin silicide.

It is possible to co-deposit TiN and TiSi₂ to form products ofintermediate properties because the reaction conditions for formingthese films are so similar. However, there is no great advantage in sodoing because TiSi₂ is a wholly satisfactory color-neutral product.

However, FIG. 2 illustrates the transparent portion of a window product108 having a titanium nitride-bearing coating on glass substrate 90 asfollows:

Coating 82: 200 angstroms of TiSi₂

Coating 84: 200 angstroms of TiN

Coating 86: 200 angstroms of TiSi₂

(The recommended protective overcoat of, say 300 angstroms of silicon ormetal oxide is recommended but not shown in FIG. 2). This productutilizes TiN to improve the solar shield properties of the device. TheTiSi₂ layers serve, not only their solar-shielding properties, but alsoserve to effectively mute the objectionable yellow tone that is apparentwhen a TiN-coated window is viewed by reflection.

A reactor system may be used as shown in U.S. Pat. No. 4,535,000 toGordon or as described in FIG. 1 of this disclosure.

Referring to FIG. 3, it is seen that coating apparatus 10 is arranged toreceive a hot glass sheet along a process line which, for example, canbe a float-glass-type processing line.

Apparatus 10, best mounted in a float-glass process housing, comprisesan entry port 12 for glass sheet 14, a first coating-reactor zone 16, asecond coating-reactor zone 18, and a glass exit port 20. Coatingreactor zones 16 and 18 are supplied with a gaseous reaction mixture viagas inlet manifolds 22 and 24, respectively and gas feed orificies 26and 28 respectively. The reactant mixture supplied via the flowpathcomprising manifold 22 and gas feed orifice 26 provides a reactionmixture which flows countercurrently along the glass in zone 16progressing towards gas outlet port 30 and gas outlet manifold 32.

The reactant mixture supplied via a flowpath comprising manifold 24, andgas feed orifice 28 is a reaction mixture which flows concurrently alongthe glass in zone 18 progressing towards gas outlet port 34 and gasoutlet manifold 36. Each reactant mixture is so selected that itdeposits a thin coating of the appropriate thickness. However, thecoating formulation should be modified as described herein. The reactionmixtures are selected so that they will be substantially depleted beforereaching the gas outlet ports.

The overall length of the apparatus from gas inlet to gas outlet isconveniently selected to be about 12 inches. The apparatus is suspendedfrom, or mounted on, support pipes 38. The reaction rates and otherreaction zone conditions are substantially improved by maintaining thosesurfaces of apparatus 10 which are in the reaction zone at a relativelylow temperature to inhibit deposition of coating material thereon. Thus,cooling fluid, say nitrogen gas, is fed into each of two coolingchambers 40, each associated with one of reaction zones 14 and 16. Thecooling gases enter through ports 42 in cooling supply pipes 44. Thegases are removed from the coating apparatus 10 at exit port 46.

The space proximate the glass at entry port 12 and exit port 20 isbrought as close as is practical to glass sheet 14 to minimize leakage.However, when the reactants are properly selected so that they neareffective depletion of silane and titanium tetrachloride reactants closeto the exit port and entry port, respectively, this sealing is notparticularly critical to the process. Thermal insulation 56 helps tomaintain the proper temperature for operation of the apparatus byseparating the hot gas outlet manifold from the gas cooled housing 54.In practice the apparatus is suitably positioned to provide about0.25-inch height to the gas flow over the glass substrate. Molten tinsupports the glass as it moves along the processing line in the mannerwell-known in the glass-making industry.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which mightbe said to fall therebetween.

What is claimed is:
 1. A process for rapid formation of a color-neutraltitanium silicide coating formed on a transparent glass substrate whichincludes:(1) maintaining the glass substrate at a temperature of aboveabout 1100° F. but below the softening point of said glass substrate;(2) feeding into a reaction zone above said glass substrate a gaseousmixture formed of(a) titanium tetrachloride; (b) a silane; and (c) aninert gas (3) heating mixture with heat from said glass substrate; (4)contacting said glass substrate with said gaseous mixture; and (5)depositing a coating of color-neutral titanium silicide thereover at arate of about 300 angstroms per second.
 2. A process as defined in claim1 including maintaining the molar concentrations of the gases fed to thereaction zone at(a) about 1% TiCl4 (b) about 3% SiH4 (c) a balance of aninert gas comprising at least 50% of heliumand maintaining the reactionzone at about 1200° F.
 3. A process as defined in claim 1 whichincludes:annealing said glass sheet at a temperature in excess of 1,000°F.
 4. A process as defined in claim 1 which includes:tempering saidglass sheet at a temperature in excess of 1,000° F.
 5. A process asdefined in claim 1 which includes:overcoating said titanium silicidewith a protective coating comprising silicon or a metal oxide selectedfrom the group consisting of alumina, silica or tin oxide.
 6. A processas defined in claim 5, wherein said coating and overcoating steps arecarried out within the reducing atmosphere of a tin float bath enclosureof a float glass production line and upon glass sheet formed in said tinfloat bath.
 7. A process as defined in claim 5, wherein the protectivecoating is about 100 to 400 angstroms thick.
 8. A process as defined inclaim 5 which includes:coating the first two layers with a second layerof titanium silicide.
 9. A process as defined in claim 8, wherein eachof the three layers is about 200 angstroms thick.